Spray guns are widely used in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. In the known spray guns, the liquid is contained in a reservoir attached to the gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomised and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed, suction fed or, more recently, pressure fed by an air bleed from the compressed air source to the reservoir.
A typical paint finish may require application of a primer, base coat and top coat. The spray gun and reservoir have to be thoroughly cleaned when changing the liquid in the paint pot to avoid cross-contamination which may adversely affect the finish. This is especially important when spraying part of a vehicle to match exactly the colour of the existing colour of the adjacent bodywork.
Cleaning the spray gun and reservoir is time consuming and often requires the use of solvents that are costly and may present a health hazard to the operator. In order to reduce the amount of cleaning and to facilitate changeover from one liquid to another, we have previously proposed in WO 98/32539 an arrangement in which the liquid is contained in a collapsible reservoir that functions as a disposable lining for a paint pot.
In one construction, the reservoir comprises an open-ended container that is a close fit in the paint pot, and a separate lid that closes the open end of the container and has an outlet connectable to the spray gun. In use, the container collapses as the liquid is withdrawn and, after spraying, the container can be removed from the paint pot with the lid attached and thrown away. The paint pot can then be provided with a new, clean container for a different liquid to be applied as the next coat. As a result, the amount of cleaning required is considerably reduced and the spray gun can be readily adapted to apply different liquids in a simple manner.
With this arrangement, the reservoir has to be detached from the spray gun and the lid removed if it is desired to top-up the reservoir with more liquid. For example when painting a large area or applying several coats of the same liquid to the same or different vehicles such as when using a primer or lacquer finish. This is time consuming and can be messy if the liquid is spilt. Also, detaching the reservoir from the spray gun and removing the lid to add more liquid to the reservoir increases the risk of contamination from other sources, e.g. dust or dirt. Unwanted solid particles can be removed by the inclusion of a filter but this may become blocked and does not prevent the colour of the finish being adversely affected by any contaminants being absorbed into the liquid.
Another arrangement for lining a paint pot to reduce the amount of cleaning is disclosed in U.S. Pat. No. 5,582,350. In this arrangement, the paint is contained in a collapsible bag within the paint pot and is connectable via an outlet at one end of the pot to a spray gun. The other end of the pot is closed by a lid that is removable to provide access to the bag within the pot. The bag has a re-sealable zipper closure by means of which paint can be added to the bag. The bag is initially connected to the outlet while empty. Paint is then poured into the bag and the bag sealed before securing the lid to close the pot. On completion of spraying, the bag can be removed for disposal and replaced by a new clean bag. With this arrangement there is a risk of spillage if the bag is overfilled before fastening the zipper closure. Furthermore, if it is desired to add paint to the bag in use, access to the zipper closure is only possible if the lid is removed to open the pot. Moreover, a collapsed or partially collapsed bag may have to be extended before opening the zipper closure to add paint and the bag may be disconnected from the outlet. As a result, paint may leak from the bag necessitating cleaning of the pot when the bag is removed on completion of spraying. This arrangement is therefore generally only suitable for single use in which the bag is filled once on initial set-up of the spray gun and is not intended for re-filling the bag.